1. Field of the Invention
A subject-matter of the present invention is a pulverulent sorbitol of low hygroscopicity and of high specific surface which furthermore exhibits a low relative density, a specific particle size and an excellent ability to flow.
The invention also relates to a pulverulent sorbitol, the technical properties of which for use in direct compression are improved, and to a process for its preparation.
2. Description of the Prior Art
Sorbitol is a hexitol mainly used in the fields of food and pharmaceutical applications as a sweetening agent but also for its reduced calorific value and its acariogenicity.
Pulverulent sorbitol, just like other pulverulent polyols, such as xylitol or mannitol, is, for its part, commonly used as a pharmaceutical excipient, as a sweetener and texturizing agent in the food industry, and as an additive vehicle in industries of all types. However, it is a better excipient than xylitol and mannitol, in particular in compression, because of its specific ability to crystallize in the form of needle-shaped crystals which are directly compressible.
Generally, in order to have available a crystalline sorbitol of high compressive strength, every effort is made to manufacture a sorbitol of .gamma. crystalline form (the .alpha. and .beta. forms are particulary unstable) by processing a supersaturated solution of sorbitol, the .gamma. form of which represents at least 90%. However, even when it is crystallized in this, most stable, .gamma. form, the pulverulent sorbitol obtained conventionally exhibits a number of disadvantages, including that of being very hygroscopic.
This high hygroscopicity has the effect of rendering the flow of pulverulent sorbitol difficult, indeed even impossible, as soon as water uptake has occurred. Its use in direct compression is then found to be limited by this, requiring, for example, serious difficulties to be overcome in filling presses in the manufacture of lozenges or tablets.
In order to avoid this flow problem of pulverulent sorbitol, the preparation has been recommended of a sorbitol of low relative density and of coarser particle size, as disclosed in Patent FR 1,506,334.
However, it is established that the lower the bulk density of a pulverulent sorbitol, the greater the friability of the latter, that is to say the greater its sensitivity to a detrimental change in its particle size by mechanical action. In addition, the dissolution times of this pulverulent product of coarse particle size are generally too long and therefore unsuitable.
Finally, while the ability to flow is partially improved by the use of particles of such a particle size, the residual hygroscopic nature, which is still too high, in all cases renders the use of this pulverulent sorbitol out of the question when it is used in combination with ingredients or additives which are very sensitive to water.
It is also established that the ability to fix significant amounts of additive is a direct function of the specific surface of the said particles. The absorption capabilities of pulverulent sorbitol thus increase in proportion as its specific surface increases. However, it is known that the specific surface of the dense crystals of commercial .gamma. sorbitol is very low. Thus, for a particle size of between 500 and 1000 .mu.m, it is very low, i.e. at most equal to 0.7 m.sup.2 /g.
With the aim of preparing a pulverulent sorbitol exhibiting an improved particle size and a good ability to flow and satisfying the desired conditions of compressibility and friability, Patent Application FR 2,622,190 discloses a sorbitol powder comprising particles with a mean diameter of between 300 and 500 .mu.m. However, the high bulk density and the relatively low specific surface of the said particles, of the order of 0.9 to 1.2 m.sup.2 /g, are not in fact significantly modified by the manufacturing process employed, so that the pulverulent sorbitol thus obtained retains the same moisture absorption factor and the same solubility in water as the starting sorbitol powder.
Patent EP 32,288 discloses a .gamma. sorbitol polymorph, with a disintegrated and loose crystalline structure, which exhibits an improved hygroscopicity and satisfactory compressive properties. However, these specific properties only relate to a particle size fraction of between 250 and 841 .mu.m (i.e. 20/60 mesh), the specific surface of which is, in any case, less than 2 m.sup.2 /g.
It emerges, from everything which precedes, that there exists an unsatisfied need to have available a pulverulent sorbitol which simultaneously exhibits the advantages, generally incompatible, of low hygroscopicity, on the one hand, and of high specific surface, on the other hand, or of low bulk density, on the one hand, and of low friability, on the other hand, for a relatively low particle size.
There is therefore a need for a novel pulverulent sorbitol capable of reconciling all of the aforementioned objectives.